Although the invention is by no means limited to use in connection with pneumatic tires, it finds one of its most advantageous uses as a pressure indicating device forming a part of the valve stem of a pneumatic tire and thus forming in effect an integral part of the inflated tire. As will be apparent hereinafter, however, the basic concepts of the invention are applicable to a wide range of pressure indicating functions.
It is well known, of course, that proper inflation of pneumtic tires is not only essential to a realization of adequate tire life, but also to the obtaining of optimum fuel efficiencies. In addition, maintenance of adequate tire inflation, can be quite important from a safety standpoint. Typically, the determination of proper inflation pressure in a tire involves considerable inconvenience to the average vehicle owner, and often requires a special trip to a service station. As a result, drivers tend to be neglectful of maintaining proper day-to-day tire inflation.
It has been proposed heretofore to provide pressure measuring devices either for attachment to the valve stem of the tire or for direct incorporation into the valve stem, to simplify the task of regular tire pressure maintenance. While the concept of such devices has been constructive, none has found widespread acceptance with the public because of various shortcomings, such as excessive cost, lack of adequate durability under the service conditions, etc.
In accordance with the present invention, a novel and improved pressure indicating device is provided which is uniquely adapted for incorporation into, for example, the valve stem of a pneumatic tire and/or a valve stem extension. The device of the invention is of such a simplified nature as to be capable of incorporation into a valve stem or extension at extremely low cost appropriate for high volume, cost conscious markets. In addition, and equally as important, the device of the invention is extremely rugged and durable and easily capable of withstanding the service conditions to which the pneumatic tires of a typical motor vehicle are exposed.
In accordance with a more specific aspect of the invention, a novel and improved pressure indicating device is provided which comprises a pressure distensible member, formed of natural or synthetic deformable elastomer. The distensible member advantageously may be a liner of a tubular tire valve stem. In conjunction with a deformable elastomer is a cover member which, in the case of a valve stem, advantageously is in the form of a relatively stiff, tough tubular cover surrounding and supporting the deformable elastomer. The cover member is bonded to the deformable elastomer in limited areas and is formed with discontinuities, typically vertical slits, in selected, unbonded areas. When the deformable elastomer is in a contracted condition, the slits or other discontinuities in the outer cover are closed or substantially closed. However, when the elastomer is exposed to increasing pressures, it will distend causing the cover to separate at the discontinuities. In accordance with the invention the deformable elastomer and cover may be of distinctively different colors, so that the distended condition of the deformable element is readily observable after a predetermined pressure threshold is reached.
In accordance with the invention, the pressure threshold at which the device provides a visible indication of change may be readily varied to suit desired end results by appropriate selection of the elastomer in the first instance and by controlling the physical dimensions and configuration of the component parts.
In one highly specific form of the invention, the indicating device is incorporated directly into a valve stem of a type designed for insertion into a motor vehicle wheel rim, for association with a conventional tubeless tire, for example. In another specific form, the device may be incorporated into an extension device, which attaches to an otherwise conventional valve stem. In the latter case, the desired pressure threshold of a tire may be quickly changed by exchanging extension elements.
In its broadest concepts, the device of the invention may be applied in a wide variety of ways for the detection and indication of predetermined pressure thresholds in any kind of pressure vessel or containment.
For a more complete understanding of the above and other features and advantages of the invention, reference should be made to the following detailed description of a preferred embodiment and to the accompanying drawings.